Fomer secretary of State Hillary Rodham Clinton speaks May 8 at an event hosted by The Pacific Council on International Policy in Los Angeles. / Frederic J. Brown, AFP/Getty Images

by Oren Dorell, @OrenDorell, USA TODAY

by Oren Dorell, @OrenDorell, USA TODAY

A State Department whistle-blower says she was threatened after turning over documents to a U.S. senator that alleged coverups of investigations into employee use of drugs and prostitutes, her lawyer says.

The whistle-blower's allegations have led lawmakers on Capitol Hill to look into whether the State Department squelched investigations into criminal behavior by employees, including an ambassador who allegedly propositioned prostitutes in a Belgian city park.

Rep. Ed Royce, chairman of the House Foreign Affairs Committee, sent a letter Tuesday to Secretary of State John Kerry asking for a briefing about the allegations detailed in recent news reports.

"The notion that any or all of these cases would not be investigated thoroughly by the Department is unacceptable," Royce said in the letter.

The allegations were revealed after Aurelia Fedenisn, a former investigator at the State Department's Office of the Inspector General, complained to Sen. Ted Cruz, R-Texas, that senior State Department officials interfered with investigations she was involved in, and then caused a report about the interference to be watered down.

Dallas lawyer Damon Mathias, who represents Fedenisn, said Fedenisn hired him after two diplomatic security agents spoke in a threatening manner to her teenage children at her home in a Virginia suburb of Washington. The agents arrived at the home to talk to Fedenisn about documents Fedenisn had given to Cruz and told the teens that they demanded to speak to their mom immediately, Mathias said.

Royce said he instructed his staff to investigate. At least one other committee is also investigating, according to a senior congressional staffer who was not authorized to speak on the record.

State Department spokeswoman Jen Psaki told reporters Tuesday that the allegations are based on a memo that was written "without the benefit of reviewing any case files, (and) included a number of unsubstantiated accusations."

"The notion that we would not vigorously pursue criminal misconduct is not only preposterous, it's inaccurate," Psaki said.

Fedenisn had turned to Cruz after she learned that an investigative report she helped write before she retired in December lacked many investigative details when it was published in February, Mathias said.

Mathias says Fedenisn's claim is that agents from State's Diplomatic Security and other divisions engaged in very questionable and possibly criminal conduct; the Inspector General has been hampered in performing its oversight role; "and the findings they wanted to put in the report end up being left out," Mathias said. "So you have a coverup of the coverup."

When Fedenisn and her lawyers met with lawyers for the Office of the Inspector General, the government lawyers demanded she hand over the documents or they would refer the matter to the Department of Justice and Fedenisn would face criminal prosecution, Mathias said.

"They made it clear that they would go after her criminally," he said.

"We refused to turn over the documents" and Fedenisn is now seeking whistle-blower protection, he said.

According to CBS News, which obtained copies of the documents Fedenisn provided to Cruz, they include a memo by the State Department's Office of the Inspector General that cites eight investigations that were "influenced, manipulated, or simply called off" during the tenure of former secretary of State Hillary Rodham Clinton.

Among the allegations CBS reported:

â?¢ A State Department security official in Beirut sexually assaulted foreign employees working as embassy guards.

â?¢ Criminal gangs sold drugs to diplomatic security personnel at the U.S. Embassy in Baghdad.

â?¢ Members of Clinton's security detail hired prostitutes while on official trips overseas.

Fedenisn told CBS those investigations were called off under pressure from senior State Department officials.

In another case, an investigation was called off into allegations that a U.S. ambassador was suspected of soliciting prostitutes in a park in Brussels, CBS reported.

The New York Post identified that ambassador as Howard Gutman, a bundler who raised $500,000 for President Obama's 2008 campaign. Gutman issued a statement Tuesday calling the allegations "baseless."

"To watch the four years I have proudly served in Belgium smeared is devastating," Gutman said. "I live on a beautiful park in Brussels that you walk through to get to many locations and at no point have I ever engaged in any improper activity."

Another allegation described in the Inspector General's memo says Clinton's chief of staff, Cheryl Mills, put the kibosh on an investigation involving Obama's nominee to be U.S. ambassador to Iraq, according to the New York Post. Members of State's Special Investigations Division never interviewed the nominee, Brett McGurk, about sexually charged e-mails between him and Wall Street Journal reporter Gina Chon because Mills intervened, the report says.

Mills advised McGurk to withdraw his name from consideration and the investigation was dropped, according to the memo.